First dungeon run last night: We encountered a locked door that neither I nor my cleric hireling could open. No problem. Once we had killed all the monsters we headed back to the nearest shrine and after a quick rest I swapped out "Melfs Acid Arrow" for "Knock" a spell which allows me to open locks.
In a second dungeon we were stopped by a door which had a minimum strength requirement to open. Again no problem - another visit to a shrine allowed me to swap in "Bulls Strength" a buff spell which gave me the strength I needed to open the door.
Versatility is the hallmark of a Wizard. Without question Sorcerers are better at casting spells. Both Wizards and Sorcerers can choose from the same list of arcane spells but sorcerers cast faster and they have more spell points which allows them to go on casting longer. Sorcerers cannot however swap spells mid mission. In fact they can only swap spells once every few days and they pay dearly to do so. Wizards can swap their spells freely in any tavern and they can swap after resting at a shrine during a mission. Shrines are on a fairly long cooldown but in an emergency there is the option of leaving the dungeon, popping into the nearest tavern and legging it back before the dungeon resets.
If you have any one job you want doing a Sorcerer can probably do it better than a Wizard. The Wizard on the other hand brings the advantage of far greater flexibility. That flexibility is a huge advantage to a solo player. As a wizard I can use spells that help make up for the lack of a rogue or a warrior in my party but a sorcerer would be unwilling to waste a valuable slot on such rarely used spells.